COMPLEXES OF IRON(III) WITH LIGANDS OF BIOLOGICAL INTEREST - DOPAMINE AND 8-HYDROXYQUINOLINE-5-SULFONIC ACID

The composition and equilibrium constants of iron(III) complexes with two bidentate ligands: dopamine (H3L+) and 8-hydroxyquinoline-5-sulphonic acid (H2L), have been studied in aqueous solution (NaClO4 mu = 1) at 25-degrees-C, with protometric and spectrophotometric methods. With dopamine, seven complexes have been obtained in the pH range 0.5-12.0. In addition to the three stepwise complexes Fe(HL)n and the three deprotonated forms of Fe(HL)3, an acidic species Fe(H2L)3+ occurs in a large pH range (0-5). 8-hydroxyquinoline-5-sulphonic acid proves to be a very good chelating agent; up to pH = 7, it is better than dopamine and most catecholate ligands.